1. Field of the Invention
The present invention relates to a method for decorating and molding three dimensional plastic articles by a technique similar to in-mold decoration.
2. Description of the Prior Art
The decoration of a variety of molded products by the application of decorating indicia to the product during the molding process, i.e., the technique of in-mold decorating, is well known. Such techniques are practiced by feeding into the mold in which the product is to be formed, a strip having one or more decorating indicia thereon. Thus, the strip would be indexed into position so that the decoration would be aligned with the intended location on the products, after which the product would be molded against the decoration. Thereafter the transferred decoration would be appropriately severed from the remainder of the strip and trimmed to complete the fabrication of the product.
The standard in-mold decorating technique possessed a variety of drawbacks to its use, particularly in high speed, continuous molding. For example, the hot transfer bearing the decorating indicia has to exceed the indicia in size, with the result that the quantitites of plastic film utilized per decoration were unnecessarily great.
Also, the disposition of additional plastic film on the final product detracted from its appearance.
Efforts to remove excess plastic film from the decoration could only be directed to post-molding operations, as pre-cutting or punching of the strip would result in the failure during the molding process due either to collapse of the strip or malalignment of the decoration with the molded product. Likewise, attempts to remove excess film from the molded product frequently result in tearing or other fracturing of the remaining indicia, or damage to the product itself, so that a high rate of rejects would develop.
The prior art with respect to in-mold decorating is exemplified by U.S. Pat. Nos. 4,059,471 to Haigh, and 4,202,663 to Haigh, deceased et al. These patents speak in passing of in-mold decoration, but concern themselves primarily with the transfer of a dye from a transfer sheet, through a polyolefin film, to a thermoplastic sheet. This is accomplished by the application of heat and pressure, causing the dye to sublime through the film and into the plastic sheet.
Similarly, U.S. Pat. No. 3,292,209 to Borkmann, and U.S. Pat. No. 3,816,207 to Robertson et al. illustrate variant apparatus utilized to the practice of transfer decoration. Borkmann is noted for its effort to develop an apparatus to practice a method disclosed in U.S. Pat. No. 3,108,580 to Brandt, wherein labels are indexed into position, and a blow-molded parison in the semi-molten state is then inflated thereagainst and heat fused thereto. Borkmann illustrates by its complexity the intricacy and precision of the apparatus that must be utilized in accordance with the prior art, to assure alignment of the decoration with the product being molded.
The criticality and complexity of in-mld decorating techniques has militated against their use in the preparation of complex decorations of the type that are now of interst to the packaging field. For example, complex decorations are now desirable for products that may include as many as three or four divergent indicia, including photographic facsimiles of a broad range of colors, appropriately trimmed with a metalized layer. The preparation of this type of complex, compound decoration requires the use of techniques such as multiple-stage printing by screen printing techniques and the like, all of which is time consuming and expensive due to the criticality in the alignment of the images of the respective components of the decoraton.
During the course of the development of the present invention, the inventors investigated the use of pre-cutting the hot transfer stock, and determined that such pre-cutting would further complicate any efforts to utilize the film for continuous in-mold decoration. In particular, the pre-cutting of the stock, either in whole or in part, resulted in failure, as the decorated portions of the stock would dislodge and could not be retained in alignment, particularly at the commercial speeds of operation of an in-mold decorating procedure.
Further investigations revealed that the area of die-cutting of transfer items was well known, but was limited in its application to pressure sensitive labels. Representative prior art patents on die-cutting, comprise U.S. Pat. Nos. 2,391,539 to Avery, 3,166,186 to Karn and 4,236,955 to Prittie. All three patents deal primarily with pressure-adhesive label stock that is disposed on a peel-away base and is appropriately die-cut by perforations or full cutting, so that the labels may be easily removed from the base for application to the intended substrate, without preliminarily adhering to themselves or to other objects before use.
Efforts to apply die-cutting techniques to plastics generally have met with failure. Particularly in the instance where the plastic films are measured in thicknesses of 3 to 10 mils, the tolerance of most die-cutting equipment is such that one cannot guarantee that the cutting edge will not strike through the first film and into the second or carrier film, and in some operations, it is this strike-through that would result in the same difficulty that one would experience if a single film were die-cut by perforation or otherwise. Clearly, then, the die-cutting techniques familiar to the label making art were investigated, and initially found to be unable to meet the rigid tolerances and requirements of the hot transfer industry.
The initial solution to the aforenoted problem was developed and disclosed in parent application Ser. No. 401,275, incorporated herein by reference, wherein a carrier film was prepared as a laminate bearing the intended decoration, and was then carefully die cut. Thereafter, the unwanted portion of the transfer was stripped away and the resulting carrier film was indexed into a mold wherein the decoration was hot transferred to the final plastic article. This technique is a radical departure from the plastic decorating techniques of the prior art as it successfully utilized the continuous die-cutting of a heat transferable indicia to facilitate continuous in-mold transfer decoration.
Recently, the present inventors have considered applying the methodology discussed above to three-dimensional products that are manufactured by insert molding. Insert molding involves the preparation of a thermoformable base to which a decorative surface such as a metallized layer is usually laminated, after which the base is shaped by heat and pressure to form the shell of the ultimate product. The shell is usually indexed into either an injection molding or blow molding chamber or the like, where the remainder of the final plastic article is formed against the underside of the shell.
The application of the earlier disclosed in-mold transfer technique to insert molding presents complications as critical alignment is necessary between the transfer and the insert in the mold that would be difficult to achieve and maintain on a commercial scale. The only apparent alternative in the case of insert molded products is to rely on the prior art techniques of individual alignment of the hot transfer in the mold with the insert, however, this technique is time consuming and understandably commercially impractical.
A need therefore exists for the development of a technique that facilitates the continuous decoration of insert-molded products, and if possible, that takes advantage of the in-mold decorating technique earlier developed by the present inventors.